Which type of bat is known for roosting alone and is commonly found in the West?

Keen's Bat is recognized for its solitary roosting habits and is often found in western regions. This bat species tends to prefer roosting alone, which distinguishes it from other bats that often roost in groups. Its solitary nature contributes to its unique behavior and habitat preferences.

In contrast, the other options listed typically have different social structures or habitat preferences. For instance, the Red Bat is known to roost in vegetation, sometimes in small groups, while the Silver-haired Bat and Hoary Bat often roost in trees or in communal settings. Therefore, identifying the Keen's Bat as the one that roosts alone reinforces its specific ecological niche within the Western landscape.